As someone who bought a used bike to start out, I'll provide the counter-point.

If you're going to get a used bike, expect to learn how to maintain it. The advantage of a new bike is that many shops provide some level of service and repairs at little to no cost for new bikes.
Think of bikes like cars, the older the bike the more likely it is to have minor issues.

The other thing with buying a used bike is that you have to know what you want and what to look for. If you're just starting out that's very difficult.